The invention relates to a device for absorbing energy during impact. The invention relates more particularly to a device for absorbing energy during impact, which is to be mounted in a motor vehicle.
In order to absorb the energy released by side impact on the door of a motor vehicle, it is known to place an impact-absorbing element inside the door. This impact-absorbing element is designed to observe a biomechanical corridor. A biomechanical corridor is understood to mean a corridor defined between an upper curve and a lower curve which are represented in a plane of which the abscissa is the penetration of the test dummy""s pelvis into the door and the ordinate is the force of the door on the test dummy""s pelvis. Each manufacturer defines his own biomechanical corridor. For example, each of the two curves is composed of a first straight line passing through the origin and a second straight line parallel with the abscissa and forming a plateau. If the curve of the absorbing element is higher than the upper limit curve, the absorbing element is too rigid and the dummy""s pelvis will be subjected to too large a force relative to the car manufacturer""s criteria. If the curve of the absorbing element is lower than the lower limit curve, the absorbing element will be supple, but the high degree of penetration of the pelvis into the door resulting from that suppleness will generate inadmissible conditions of contact between the upper portion of the door and the abdomen, torso and head of the test dummy.
A first type of absorbing element in the form of a block of foam is known. The space inside the door which has to be filled by the foam is large. The width to be filled may typically be 120 mm. Since foam is an expensive material, the result will be a high cost which is incompatible with the majority of categories of vehicle.
Another type of absorbing element is based on deformable injection-moulded plastics elements. That type of absorbing element includes ribbed compartments. However, discontinuities in the biomechanical curve are observed owing to the non-optimised random breaking of the ribs.
That same type of deformable injection-moulded plastics element also includes compartments having conical impact-absorbers. Those compartments, which are described, for example, in FR 2784151, comprise a plate from which rises a plurality of frustoconical, hollow, impact-absorbing elements, each absorbing element exhibiting crushing resistance. The major disadvantage of those structures having conical impact-absorbing elements results from their excessive height (120 mm) which may lead to a buckling of the whole structure during impact. Another disadvantage of that type of structure results from the angle condition of the truncated cone which must be from 10 to 15 degrees for optimised mechanical strength. Owing to the great height, the truncated cones corresponding to the angle condition have a large base of major proportions limiting the number of truncated cones per structure.
One of the objects of the present invention is to propose an absorption device of the deformable injection-moulded plastics element type, which overcomes the disadvantages mentioned above.
Another object of the present invention is to propose an absorption device, the manufacture of which is simple and economical.
For those purposes, the invention relates to a device for absorbing energy during impact, comprising a plurality of hollow impact-absorbing elements, each absorbing element having a crushing resistance. According to the invention, it comprises two base plates facing one another, a portion of the plurality of impact-absorbing elements rising from each plate, and the impact-absorbing elements of one plate rising in a direction opposite that of the impact-absorbing elements of the other plate.
Advantageously, the absorbing elements have a frustoconical shape.
According to another feature according to the invention, the large base of the absorbing elements is elliptical.
In one embodiment, the bases of the absorbing elements of one plate are offset relative to the bases of the absorbing elements of the other plate.
Advantageously, the offset is angular.
In one embodiment, each absorbing element of one plate corresponds to an absorbing element of the other plate, the absorbing elements being coaxial in the direction of an impact axis and being offset angularly relative to one another about that impact axis.
In order to simplify manufacture and assembly, the absorbing device is moulded in a single piece and comprises a film hinge between the two facing base plates.
The invention relates also to a motor vehicle door comprising a device for absorbing impact energy arranged between an outer wall and an inner wall. According to the invention, the energy-absorbing device is a device such as described above.
A first advantage of the present invention results from the division of the absorption device of the prior art into two sub-structures. Consequently, the height of the truncated cones is divided by two, which multiplies the overall critical buckling load by four. That substantially reduces the risk that the absorption device will buckle in the case of impact.
Another advantage of the present invention results from the ellipsoidal or oblong shape of the large base of the truncated cones. This feature enables the facing absorbing elements to be offset in such a manner that a not inconsiderable portion of the periphery of the large base of one of the absorbing elements rests on the plate of the other absorber.